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Thread: 4g63 running issues. runs rough and revs up and down for 30seconds then runs backward

  1. #1

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    1991 Mitsubishi Mighty Max
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    4g63 running issues. runs rough and revs up and down for 30seconds then runs backward

    i did and direct engine swap in my 1991 mitsubishi mighty max. engine is a 4g63 2.4l. did a new timing belt and water pump before i set motor in. When i start the engine it runs very rough and only runs for about 30 seconds. The engine will run at low rpm then surge to a higher rev over and over again for thirty seconds. then on downside of the last surge of rpms the engine will spin backwards and die. i have triied playing with the distributor and that hasnt changed anything. looks like i have everything connected correctly. i am stumped. driving me nuts. anyone have any ideas?

  2. #2

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    Idle speed controller, of the Fast Idle airflow valve, both located on the lower portion of the Throttle body.

  3. #3

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    thanks. will try that. do you think it could have anything to do with vaccum hoses?

  4. #4

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    o and by the way the motor is 64 not 63. typing error

  5. #5



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    It's all vacuum and timing. The timing is off some where, that makes it run backward, to advanced. The belt might be off 1 tooth or 1 on the dist. I know you don't like to here that but there is somthing wacky going on there. My concrete pump guy has a diesel that will run backward when it gets stalled and cranked backward by the hydraulic system. But it will continue to run that way tell you shut it down. Direct injection of fuel. Yours will only run that long until the fuel it can burn in the exhaust is gone. That tells me that somthing is wrong on the vacuum lines.
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  6. #6



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    Just think, if we could reverse our engine running, we could toss out the reverse gear in the transmission,

    Do you have a balance shaft also, was a new belt replaced on this too? Make sure the balance shaft was properly set installing that belt. As far as engine running backwards, I think Camoit hit it right with a misalignment with belt or distributor. It's not as complicated as it seems to install a belt and maintain timing, yet it is very easy to get it wrong and set up frustration. Timing light available? Check number 1 piston TDC to number 1 distributor cap plug wire location on compression stroke. Vaccum leaks could be an issue, but as bad as it seems to be, you'd think you could hear the hiss from such a leak.
    Belt check would be first, making positive it is correct.
    then check dizy position, this can one tooth or 180 degrees off very easily.
    Vaccum leaks-only leak that should be happening is the big fat one down the carburetor throat, lol.
    Last edited by BradMph; 05-03-2013 at 04:41 PM.

  7. #7

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    Thank you guysm will check it all. It is very frustrating. Will check all vacuum lines and timing. Also this is a 4g64. I made a typo. It has a throttle body not a carb. Will see what happens

  8. #8

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    I got the motor running without the rev surges. and also this is not a carburated model. it still seems like it is misfiring and the engine does not respond well when you give it some throttle. it seems to bog when you give it throttle

  9. #9

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    I have that same problem in mine. What's weird, the truck will give a hard time starting and the engine is not firing or turning over. When it does that, it won't start.
    Even when it's cold does that. Other times, the truck starts. And then there's smoke.

  10. #10



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    Timing mark should look like this.
    http://www.mightyram50.net/vbulletin...am-Timing-Mark
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  11. #11

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    try changing the spark plugs. mine did that too.

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